Sliding members are used in various fields such as bearing member, rolling roll material, vane for compressor, gas turbine blade, cam roller and so on. For the sliding members, a ceramic material that is lightweight and has high strength is increasingly used. In particular, a silicon nitride sintered compact is excellent in mechanical strength and abrasion resistance and therefore progressively applied to bearing members such as a bearing ball.
For the bearing members such as the bearing ball and so on using the silicon nitride sintered compact, it has been proposed to improve the sliding characteristics represented by the mechanical strength and rolling life, for example, based on control of the sintered compact composition (the kinds, the addition amounts and so on of sintering aids), control of forms of the aid components in the sintered compact, control of manufacturing process and so on (see Patent References 1 and 2). Patent Reference 1 describes a silicon nitride sintered compact containing, as sintering aids, rare earth elements of 2 to 10 mass % in terms of oxide, spinel of 2 to 7 mass %, silicon carbide of 1 to 10 mass %, and at least one kind selected from among Ti, Zr, Hf, W, Mo, Ta, Nb and Cr of 5 mass % or less in terms of oxide.
Incidentally, in electronic equipment having a disk medium such as an HDD, DVD or the like, its rotation shaft is rotated at a high speed by a spindle motor to work the disk mounted on the rotation shaft. It is tried that a bearing ball made of the silicon nitride sintered compact that is lightweight and has excellent abrasion resistance is applied to a bearing of the rotation shaft rotated at a high-speed. However, the bearing ball made of the silicon nitride sintered compact is inferior in thermal conductivity to a conventional bearing ball made of metal, and therefore has a drawback of being incapable of efficiently releasing heat generated by the high speed rotation of the rotation shaft to the outside.
Further, it has also been tried that the thermal conductivity of the silicon nitride sintered compact is enhanced (see Patent References 3 and 4), but only the enhancement of the thermal conductivity may sacrifice the sliding characteristics. On the other hand, for the silicon nitride sintered compact used for amounting board and a heat sink of various electronic parts, a silicon nitride sintered compact enhanced in thermal conductivity by using a silicon nitride powder having reduced oxygen content and reduced amount of impurity positive ion elements has been proposed (see Patent Reference 5). However, the silicon nitride sintered compact for electronics parts that is applied to the mounting board and heat sink does not have sufficient abrasion resistance. Therefore, the silicon nitride sintered compact for electronic parts cannot be directly applied to the sliding members such as the bearing member and so on.
Patent Reference 1: JP-A 2003-034581(KOKAI)
Patent Reference 2: JP-A 2006-036554(KOKAI)
Patent Reference 3: JP-B 3445342 (Patent Publication)
Patent Reference 4: JP-A 2000-034172 (KOKAI)
Patent Reference 5: JP-A 6-135771 (KOKAI)